The invention relates to a trailer hitch for vehicles, especially for motor vehicles, which hitch comprises a mounting support including a support tube for connection to the vehicle and a ball carrying bar which is received and detachably mounted in the support tube.
Vehicle trailer hitches of this type are known, for example, from the German DOS Nos. 1655012 and 3004285. With the hitches disclosed therein however it is necessary to manually insert a safety bolt into the support tube for locking the ball carrying bar in engagement with the support tube. This is considered to be a disadvantage. Also it is noted that omission of the locking procedure or mere partial insertion of the safety bolt results in trailering operations with such hitch that are unsafe.
An arrangement as disclosed in German DOS No. 3327051 tries to overcome the disadvantage pointed out above by providing a spring-loaded safety bolt providing a force which retains the safety bolt in its locking position. In order to compress the spring, there is provided a lever adapted to act on an operating ring which lever needs to be operated in order to disengage the ball carrying bar from the support tube and which, at the same time, causes the compression of the spring. Upon insertion of the ball carrying bar into the support tube, that is, when the spring is to move the safety bolt into its locking position, the operating ring and together therewith the operating lever are pivoted. During this operation it is however possible that movement of the operating ring and the operating lever is obstructed by foreign objects so that the safety bolt will not assume its fully inserted locking position without this fact being noticed by the operator.
An improvement is provided by the arrangement according to the European Patent Application No. 84 108 847.9 wherein, unlike with the arrangement according to DE OS No. 3327051 in which the spring force is applied to the locking bolt via an operating ring and a detent structure disposed therein, the spring force is utilized to rotate an eccenter shaft which is adapted to move the safety bolt into its end position. The arrangement as disclosed permits the use of a relatively small operating lever for the compression of the spring which lever may be so arranged that it is tiltable such that rotation of the eccenter shaft or rather insertion of the safety bolt cannot be obstructed.
It is pointed out however that, with all these arrangements, a part of the operating forces acting on the ball carrying bar, especially the push and pull forces acting in longitudinal direction of the ball bar, have to be taken up by the safety bolt. While the safety bolt may of course be made strong enough such that operational safety of the system is not directly jeopardized, it would be appropriate if the safety bolt would not at all be subjected to operational forces and would serve only to secure the ball bar in a position in which the ball bar is adapted to directly transmit forces to the support tube.
The arrangement according to DOS No. 1655012 is safe for its intended use if the safety bolt is properly positioned in its lock position but it is not rattle free. With this arrangement there is some clearance between the cavity on the ball bar and the safety bolt which permits back and forth movement of the ball bar within the support tube so that with each change of direction of the load on the ball bar there is a jerk on the support tube and the vehicle which results not only in a dynamic load of the parts but also in noise and an annoying sensation to the driver.
In all designs described so far, the ball bar is externally locked by the safety bolt. The height of the whole design is therefore determined by the height dimension of the support tube plus any additional dimensions of the safety bolt. However the space available for mounting of a hitch together with its support tube on a vehicle is very limited especially as far as height is concerned so that frequently problems are encountered when hitching structures are to be mounted on vehicles.
It is therefore an object of the present invention to provide a trailer hitch with reduced design height requirements when compared with prior art arrangements.
It is also an object of the invention to provide a hitch design wherein, upon insertion of the ball carrying bar into the support tube, the safety mechanism is activated by automatic movement of a safety bolt into its end position without the need for manual activation and without the danger that operation of the safety mechanism is inhibited by any means that may come into its path of movement particularly not by dirt or corrosion deposits. Also, the safety member should not be subject to any operating forces acting longitudinally on the ball bar or the support tube, that is, it should serve only to insure engagement of the ball bar with the support tube.
It is finally a further object to provide a hitch arrangement which remains free of rattles over its lifetime.